This invention relates to a resistance welding electrode for welding fasteners to a metallic object, and more particularly, the invention relates to an insulated stop for limiting electrode pin travel.
Weld gun assemblies are used to resistance weld fasteners to metallic objects such as body panels for vehicles. A fastener such as a weld stud or nut is loaded onto one of the electrodes. The electrodes are moved together with an actuator placing the fastener into engagement with the panel under pressure. Very high currents are applied to the electrodes, which welds the fastener to the panel. The use of weld guns is typically an automated process in which the fasteners are loaded into the weld gun assembly. Occasionally, the fastener is not properly loaded into the weld gun, which under, certain circumstances may cause damage to the electrode.
A widely used electrode in the industry utilizes a pin that receives a weld nut. The pin is biased to an extended position to receive the weld nut. The pin must be insulated from the electrode to prevent arching. If arching occurs, the surface of the pin could be damaged and prevent the unrestricted travel of the pin. Furthermore, a portion of the welding current will flow through the pin instead of the intended path through the nut and panel and the threads of the nut might be welded to the pin. Typically, a spring is employed in a bore in the electrode housing to bias the pin. During welding, the pin is moved to a depressed position in which the spring becomes compressed. If the weld nut is not properly loaded on the electrode, components of the electrode may become crushed or cracked. For example, if the weld nut was incorrectly loaded on the pin such that it was on top of the pin instead of being engaged on the pin with the pin extending through the weld nut hole, the opposing electrode will apply an excessive force to the electrode components. The pin may depress the spring to the point of failure and may also crack the spring insulator.
The pin must remain insulated from the electrode throughout the welding operation, even during improper operation of welding unit such as an improperly loaded pin. Because the dimensions of the electrode components have been standardized in the industry, it is not possible to lengthen the electrode body to accommodate features that would prevent excessive force from being applied to the spring and spring insulator. For example, modification to the pin or extensive modification to the electrode housing may not be possible. Therefore, what is needed is an improved resistance welding electrode that prevents damage to the spring and spring insulator due to excessive force from an improperly loaded weld nut.
The present invention provides a welding electrode for welding a fastener to an object. The electrode includes a housing assembly with a bore disposed in the housing assembly. A pin is disposed within the bore and is movable along an axis between extended and depressed positions. The pin is retained in the bore by a flange on a lower portion of the pin that extends radially outwardly. A spring is arranged within the bore and urges the pin from the depressed position to the extended position in which a weld nut may be loaded onto the pin. The spring has a compressed length indicative of a spring failure. A stop such as a spring insulator is arranged within the bore adjacent to at least a portion of the spring. The stop extends generally longitudinally in the direction of the pin axis. The stop defines a maximum spring compression length in a fully depressed pin position that may be caused from an improperly loaded weld nut. The maximum spring compression length is greater than the compressed length so that the spring does not become compressed to the point of failure. The stop is preferably constructed from nylon and has a length sufficient to accommodate excessive forces on the stop caused by an improperly loaded weld nut.
Accordingly, the above invention provides an improved resistance welding electrode that prevents damage to the spring and spring insulator due to excessive force from an improperly loaded weld nut.